At present, radial tires are an assembly of a series of components including a carcass, belt, cap ply—which are all embedded in rubber—and a rubber tread. The tire carcass conventionally supports the circumferential rubber tread which also contains a circumferential belt ply between the tire carcass and tread composed of, for example, a cord reinforcement which can be, for instance, a filamentary steel cord.
The carcass is usually formed from steel cords in truck tires and polymer yarn in the case of passenger car tires. The belt can be composed of one or more layers of plies of tire cords that are steel cord, glass fibres, polyester, nylon, aramid or rayon. The belt is positioned in the crown region of the carcass and interposed between the carcass and the cap ply. The cap ply usually consists of textile cords although steel cord reinforced cap plies are being developed (see e.g. EP1332894, WO 2003/008207).
Each component in the tire construction has a specific function in the service and performance of the final product. For instance, the belt plies act to restrict the movement of the tread and give the tire better road-holding and handling properties. Support of this type is particularly important in a radial tire where the carcass is formed from a rubberized woven fabric having relatively inextensible reinforcement cords running transversely, i.e. radially from bead to bead. The function of the cap ply is to protect the steel belts from delaminating by centrifugal force and especially when the movement of the steel cords of the belt plies at higher speeds creates excessive temperatures in the tire.
Problems with the current belt construction are well known in the industry. The belt ply is now manufactured by cutting an array of rubber encased steel cords at an angle and splicing these pieces together to form a continuous array of steel cords at an angle to the equator of the tyre. A drawback of the present design of the belts is that the steel cord ends can cut and damage the neighbouring rubber parts during the dynamic loading of the tire in service. Furthermore, the cut ends—showing bare steel—do not adhere well to rubber and can be subjected to corrosion. These negative effects appear at the edges of the carcass layer and can affect the lifetime of a tire by a failure mode commonly known as ‘belt edge separation’.
An example for the architecture of belt plies can be found in U.S. Pat. No. 5,695,578. Here, it is described that two belt plies are each made from a first and a second series of cords of different material. The cords are alternated with each other axially across the width of the tire according to a preestablished sequence. The different materials cooperate with each other to withstand tensile stresses in the longitudinal direction. However, the belt plies of this example still are cut at the edges involving the drawbacks induced by that mentioned above.
On the other hand, JP10258609 describes a belt ply that comprises of continuous steel cord which is coiled and where the coils sequentially and partially overlap. The resulting band of coils is then disposed between upper and lower rubber sheets. Like that, cut edges are avoided but the coiled belt ply structure of JP 10258609 A has a variety of other drawbacks especially in view of the production because the coils of steel cord tend to twist around each other and can easily be displaced in the process of being incorporated between the rubber sheets. Moreover, fretting of the overlapping parts of the coils can cause problems as well due to a possible local built-up at the large overlap areas.